In the course of manufacturing zippers, it is common practice to coat them with a variety of materials and for a number of reasons, such as to color or otherwise improve or modify their appearance, to afford protection against corrosion or the like, and to facilitate operation, e.g., by providing low-friction surfaces thereon. Conventionally, the coatings are produced by applying the material as a liquid; however, such an approach is often difficult, disadvantageous, or unfeasible. Thus, it is difficult to limit the coating to those areas on which it is desired (i.e., the teeth but not the fabric) while at the same time producing adequate coverage, especially on obscured surfaces lying between the teeth. In other cases, the coating material may not be suitable for application in liquid form, either because it does not readily dissolve or melt, or because the solvent or heat involved would have a deleterious effect upon the zipper. For example, when the fabric web is made from a heat-sensitive material, it may not be feasible to apply the coating as a melt, depending, of course, upon the temperatures involved. Similarly, a technique in which the deposited material requires post-heating may not be feasible when the web material is incapable of withstanding the elevated temperatures to which it would normally be subjected.
Accordingly, it is a primary object of the present invention to provide a novel method and apparatus for continuously coating a zipper chain with a heat-fusible particulate coating material.
It is also an object of the invention to provide such a method and apparatus whereby the coating may be produced on a zipper chain which includes a web made from a fabric that is adversely affected by exposure to elevated temperatures.
Another object is to provide such a method and apparatus whereby the coating is produced uniformly upon substantially all exposed surfaces of the teeth of the zipper.
Still another object of the invention is to provide such a method and apparatus which are adapted for the high speed production of coatings efficiently, conveniently, and relatively inexpensively.